A process-conditioned and spatially consistent method for reducing
systematic biases in modeled streamflow
Abstract
Water resources planning often uses streamflow predictions made by
hydrologic models. These simulated predictions have systematic errors
which limit their usefulness as input to water management models. To
account for these errors, streamflow predictions are bias-corrected
through statistical methods which adjust model predictions based on
comparisons to reference datasets (such as observed streamflow).
Existing bias-correction methods have several shortcomings when used to
correct spatially-distributed streamflow predictions. First, existing
bias-correction methods destroy the spatio-temporal consistency of the
streamflow predictions, when these methods are applied independently at
multiple sites across a river network. Second, bias-correction
techniques are usually built on simple, time-invariant mappings between
reference and simulated streamflow without accounting for the hydrologic
processes which underpin the systematic errors. We describe improved
bias-correction techniques which account for the river network topology
and which allow for corrections that are process-conditioned. Further,
we present a workflow that allows the user to select whether to apply
these techniques separately or in conjunction. We evaluate four
different bias-correction methods implemented with our workflow in the
Yakima River Basin in the Pacific Northwestern United States. We find
that all four methods reduce systematic bias in the simulated
streamflow. The spatially-consistent bias-correction methods produce
spatially-distributed streamflow as well as bias-corrected incremental
streamflow, which is suitable for input to water management models. We
also find that the process-conditioning methods improve the timing of
the corrected streamflow when conditioned on daily minimum temperature,
which we use as a proxy for snowmelt processes